In order to meet the wireless data traffic demand that is on an increasing trend after commercialization of 4G communication system, efforts for developing improved 5G communication system or pre-5G communication system have been made. For this reason, the 5G communication system or pre-5G communication system has been called beyond 4G network communication system or post LTE system.
In order to achieve high data rate, implementation of a 5G communication system in an ultrahigh frequency (mmWave) band (e.g., like 60 GHz band) has been considered. In order to mitigate a path loss of radio waves and to increase a transfer distance of the radio waves in the ultrahigh frequency band, technologies of beamforming, massive MIMO, full dimension MIMO (FD-MIMO), array antennas, analog beamforming, and large scale antennas for the 5G communication system have been discussed.
Further, for system network improvement in the 5G communication system, technology developments have been made for an evolved small cell, advanced small cell, cloud radio access network (cloud RAN), ultra-dense network, device to device communication (D2D), wireless backhaul, moving network, cooperative communication, coordinated multi-points (CoMP), and reception interference cancellation.
In addition, in the 5G communication system, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC), which correspond to advanced coding modulation (ACM) systems, and filter bank multicarrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA), which correspond to advanced connection technologies, have been developed.
On the other hand, a wireless communication system has been developed from an initial one that provides a voice-oriented service to a broadband wireless communication system that provides a high-speed and high-quality packet data service, like the communication standards, such as 3GPP High Speed Packet Access (HSPA), Long Term Evolution (LTE) or Evolved Universal Terrestrial Radio Access (E-UTRA), LTE-Advanced (LTE-A or E-UTRA Evolution), 3GPP2 High Rate Packet Data (HRPD), Ultra Mobile Broadband (UMB), and IEEE 802.16e. The LTE-A is an evolved system of the LTE, and includes additional functions, such as carrier aggregation (CA) technology and higher-order multiple input multiple output (MIMO) technology, in addition to the existing LTE functions. In the present invention, unless specially mentioned, the LTE-A and the LTE are mixedly used.
In an LTE or LTE-A system that is a representative example of the broadband wireless communication system as described above, an orthogonal frequency division multiplexing (OFDM) method is adapted in a downlink, and a single carrier frequency division multiple access (SC-FDMA) method is adapted in an uplink. The uplink (UL) means a radio link through which a terminal transmits data or a control signal to a base station, and the downlink (DL) means a radio link through which the base station transmits data or a control signal to the terminal. In general, the multiple access method as described above separates data or control information for each user by allocating and operating time-frequency resources on which the data or the control information is carried for each user so that the resources do not overlap each other, that is, so that orthogonality is realized.
FIG. 1 is a diagram illustrating the basic structure of a time-frequency resource region that is a wireless resource region in which data of an LTE or LTE-A system or a control channel is transmitted.
In FIG. 1, a horizontal axis represents a time domain, and a vertical axis represents a frequency domain. The minimum transmission unit in the time domain is an OFDM symbol in the case of the downlink, and it is an SC-FDMA symbol in the case of the uplink. In this case, Nsymb symbols 102 are gathered to constitute one slot 106, and two slots are gathered to constitute one subframe 105. The length of the slot is 0.5 ms, and the length of the subframe is 1.0 ms. Further, a radio frame 114 is a time domain interval composed of 10 subframes. The minimum transmission unit in the frequency domain is a subcarrier in the unit of 15 kHz, and the transmission bandwidth of the whole system is composed of NBW subcarriers 104 in total.
In the time-frequency domain, the basic unit of a resource is a resource element (RE) 112, and it may be indicated as an OFDM symbol or an SC-FDMA symbol index and a subcarrier index. A resource block (RB) 108 or a physical resource block (PRB) may be defined as Nsymb successive OFDM symbols 102 in the time domain or NRB successive subcarriers 110 in the frequency domain. Accordingly, one RB 108 is composed of Nsymb×NRB REs 112. In the LTE or LTE-A system, data is mapped in the unit of an RBT, and the base station performs scheduling in the unit of an RB pair constituting one subframe with respect to a specific terminal. The number of SC-FDMA symbols or the number of OFDM symbols Nsymb is determined in accordance with the length of a cyclic prefix (CP) that is added for each symbol to prevent inter-symbol interference. For example, if a normal CP is applied, the number of OFDM symbols Nsymb becomes Nsymb=7, whereas if an extended CP is applied, the number of OFDM symbols Nsymb becomes Nsymb=6. NBW and NRB are in proportion to the bandwidth of the system transmission band. The data rate is increased in proportion to the number of RBs scheduled for the terminal. In the LTE or LTE-A system, 6 transmission bandwidths are defined and operated. In the case of an FDD system in which the downlink and the uplink are discriminated by frequencies to be operated, the downlink transmission bandwidth and the uplink transmission bandwidth may differ from each other. The channel bandwidth indicates an RF bandwidth that corresponds to the system transmission bandwidth. Table 1 indicates a corresponding relationship between the system transmission bandwidth defined in the LTE or LTE-A system and the channel bandwidth. For example, the LTE or LTE-A system having a channel bandwidth of 10 MHz includes the transmission bandwidth that is composed of 50 RBs.
TABLE 1Channel bandwidth BWChannel [MHz]1.435101520Transmission bandwidth configuration615255075100NRB
The LTE-A system can support the bandwidth that is wider than the bandwidth of the LTE system for high-speed data transmission. Further, in order for the LTE-A system to maintain backward compatibility for the existing LTE terminals, it is required for even the LTE terminals to receive services by accessing to the LTE-A system. For this, the LTE-A system may divide the whole system band into component carriers (CC) of the bandwidth that can be transmitted or received by the LTE terminal, and may combine several component carriers with each other to provide the services to the terminal. The LTE-A system generates and transmits data for each component carrier, and thus can support high-speed data transmission of the LTE-A system by using transmission/reception processes of the existing LTE system for each component carrier. The LTE-A system can support 5 carrier aggregations (CA) at maximum through the carrier aggregation (CA) technology, and thus it can provide wideband services reaching the bandwidth of 100 MHz (20 MHz×5) at maximum.
Recently, in order to process explosively increasing mobile data traffic, there has been a lively discussion on a 5th generation (5G) system that is the next-generation communication system after LTE/LTE-A. As compared with the existing LTE or LTE-A, the 5G system takes aim at ultrahigh-speed data services reaching several Gbps using an ultra-wide band over 100 MHz. Since it is difficult to secure the above-described ultra-wide band frequency over 100 MHz in the frequency band in the range of several hundred MHz to several GHz used in the existing mobile communication system, the ultrahigh frequency band of several GHz or several tens of GHz is considered as a candidate frequency in the operating frequency band of the 5G system.
A radio wave of the ultrahigh frequency band as described above may be called a millimeter wave (mmWave) having a wavelength at the level of several millimeters. However, in the ultrahigh frequency band, a path loss of the radio wave is increased in proportion to the frequency band, and thus the coverage of the mobile communication system is decreased.
In order to overcome the drawback of the coverage decrease of the ultrahigh frequency band as described above, a beamforming technology has become important, which increases an arrival distance of the radio wave through concentration of radiation energy of the radio wave on a specific target point using a plurality of array antennas. The beamforming technology can be applied to not only a transmission end but also a reception end. In addition to the coverage increase effect, the beamforming technology also has the effect of reducing interference in regions excluding the beamforming direction. In order for the beamforming technology to operate properly, a method for achieving an accurate measurement of transmitted or received beams and a feedback of the measured beams is necessary.
As another requirement of the 5G system, an ultra-low latency service having about 1 ms or less of transmission delay between the transmission end and the reception end is required. As one scheme for reducing the transmission delay, it is necessary to design a frame structure based on transmit time interval (TTI) that is shorter than that of the LTE or LTE-A system. The TTI is a basic unit to perform scheduling, and the TTI of the existing LTE or LTE-A system may be 1 ms corresponding to the length of one subframe. For example, as a short TTI to satisfy the requirements of the ultra-low latency service of the 5G system, the TTI of the 5G system may be 0.5 ms, 0.2 ms, or 0.1 ms that is shorter than that of the existing LTE or LTE-A system.
Accordingly, in a communication system in which the LTE/LTE-A system and the 5G system are combined to be operated, if the TTIs supported by the respective systems are different from each other as described above, it becomes necessary to define a method for a terminal to distribute uplink signal transmission power.